Excavation methods and excavators using electric pulses are known hitherto. For example, optimization for crush of a rock mass and a man-made structure by means of electric pulses is described by Vajor V. F., Siomkin B. V., Adam A. M., "Physics Vol. 4", Tomsk Polytechnic University 1996.
According to this known excavation method, a bore top is placed on a rock mass in a discharge liquid. High-voltage pulses are applied to electrodes at intervals of microsecond to allow electric discharge pass through the rock mass so as to fracture and crush it. The time required for the rock mass to be fractured is determined by a length between the electrodes. The drawback to this method is that the interval between the electrodes is only one parameter for increasing excavating efficiencies.
Another conventional type of excavator comprises a high-voltage pulse generator, a bore pipe, and a bore top. The bore pipe includes an outer earth pipe and an inner high-pressure pipe arranged concentrically and has the bore top at the tip end. The drawback to this excavator is no equipment for setting optimum conditions for excavation.
Known as a still another known excavation method and excavator is "Material crush by means of electric pulses" written by B. V. Siomkin, A. F. Uthof, V. I. Bathes (on pages 7-11, 34-62, 220-224, 11-16 and 231-240, Nauka Press 1995).
According to this method of testing, a rock mass to be crushed is dipped into a liquid. The liquid serves as an insulator in a selected pulse range of high-voltage electric pulses. The electric pulses are applied to the electrodes placed on the rock mass to allow the electric discharge to occur in the rock mass dipped in the insulating fluid. The drawback of this method is that the optimum condition for the crushing of the rock mass is only effective for the rock mass existing between the two electrodes, which is thus largely different from excavation.
A yet another known excavator comprises a bore top, a bore pipe and a high-voltage power supply. This known excavator is provided with a guide at an entrance of a hole to be excavated and a lifting device. The discharge liquid in the hole is allowed to cycle to be led to a discharge reservoir. The high-voltage pulses are applied to a high-pressure pipe of the bore pipe.
The drawback to this known excavator is that the excavating hole is not so sufficient in structure as to reach the maximum efficiency.
In the light of the above-described drawbacks involved in the prior art, the present invention has been made. It is the object of the present invention to provide an excavation method and an excavator capable of excavating efficiently with a minimum power consumption.